Many types of mufflers to muffle the exhaust sound generated from automobile engines, etc., have been used, and among those existing types, a representative type is indicated in FIG. 20, which is constructed to have for example a cylindrical muffler body to which one end is attached to an exhaust duct pipe 1' which is connected to the exhaust port of the engine at the other end, a tail pipe 2' is attached to the other end, to have their positions displacing each other, the muffler body is divided into plural number of chambers 5a, 5b, 5c, with bulkheads 4, 4, attaching exhaust duct pipe 1' to the end so that the duct pipe penetrates through the both bulkheads 4, 4 and opens to the chamber 5c, attach a tail pipe 2 to the other end so that it is staggered with the exhaust duct pipe 1' and to open in the chamber 5a, places two intermediate ducts 6, 6' to pass through the bulkheads 4, 4 so that these chambers 5a, 5b, 5c are connected, provides many small holes 7 around the wall of the aforementioned exhaust duct pipe 1' at the portion within the body, to muffle the sound by the resistance when the exhaust gas passing these small holes 7, resistance during the gas reflect its direction, and the capacities of chambers 5a, 5b, 5c.
It is desirable to reduce the exhaust resistance be as small as possible for an exhaust system to upraise the efficiency of the engine, however, there are problems that exhaust system generates resonance under small exhaust resistance, and an exhaust sound of specific frequency cannot be muffled.
So far exhaust resistance was increased by passing the exhaust gas through many small holes 7, or make the gas flow reflected to prevent the resonance phenomena as shown in FIG. 20, however, increase of the exhaust resistance accompanies efficiency reduction of the engine, and the results is not satisfactory.
The resonance phenomenon are a phenomenon that a progressing wave which is a sound wave generated in an engine traveled through the exhaust duct, muffler body, tail pipe reflects at the end of the tail pipe, becomes a reflected wave and interferes with the progressive wave, and intensifies the sound, or a phenomenon to accumulate the sound energy.
Therefore, prevention of the resonance phenomenon can be effected by preventing energy accumulation by absorbing the sound energy at some place of the exhaust duct muffler body, tailpipe, however, absorption of energy by installing resistance in the main stream of the exhaust gas such as the exhaust duct, muffler and tail pipe will increase the exhaust resistance and is not preferable, therefore this should be avoided.